Collision Avoidance for Operational ESA Satellites

Since more than 10 years the European Space Operations Centre (ESOC) has been monitoring close proximities of objects of the US Space Surveillance Network Catalog with operational ESA satellites in low-Earth orbits. In recent years this activity has evolved into an operational service which is provided for the ERS-2 and Envisat remote sensing satellites. In this paper the basic principles of a Catalog based conjunction event detection and collision risk estimation process are explained, associated orbit prediction uncertainties are addressed, operational collision avoidance procedures are outlined, avoidance manoeuvre citeria are explained, and examples of evasive manoeuvres are provided. The observed manoeuvre rate is compared with a statistical manoeuvre frequency assessment, based on collision flux predictions for Catalog size objects by ESA’s MASTER-2001 space debris environment model.